This invention relates to an exercise device for exercising all of the major muscles comprising the upper and lower abdomen and back, while avoiding undue stress on the lumbar and cervical spinal discs and the muscles comprising the lower back and hip flexors.
It is well-known in the fitness industry that exercises which can optimally strengthen and tone the principal muscles in the abdominal region preferably are specific to particular muscles and/or to portions of those muscles.
The principal abdominal muscles include the rectus abdominus. The rectus abdominus muscles are a pair of long flat muscles, on either side of the navel, which extend along the whole length of the front of the abdomen from the lower rib cage to the front of the iliac and pubic bones of the pelvis. The rectus abdominus muscles are interconnected by the linea alba, a band of fibrous connective tissue.
The principle muscles in the back include the erector spinae muscle which is composed of the iliocostalis, longissimus and spinalis muscles. These three muscles are grouped into a pair of long thick muscles running on either side of the spine for the length of the back.
The upper portion of the rectus abdominus can be effectively exercised by performing repetitions of "sit-ups" using the "crunch" technique. In this context, "crunch" refers to the motion in which the trunk of the human body is raised from a supine position, i.e., flexed, in a curling motion, while the spine is flexed so that the anterior portion of the spine is concave while the posterior portion of the spine is convex, and with the legs remaining straight or bent.
The lower portion of the rectus abdominus can be effectively exercised by performing repetitions of the "knee-up" exercise in which the knees are lifted in an arcing motion toward the chest wall. "Knee-up" exercise refers to that motion of rotation of the legs, with the knees facing up and bent, and while the person is lying on the ground or floor.
The muscles of the back can be effectively exercised by performing a "reverse-situp," where the individual is supported above the ground in a fashion to allow the body to bend at the waist with the head hanging down. The individual then raises the head and body to an erect (albeit horizontal) position.
A primary concern during abdominal and back exercises is the motion of the vertebrae of the spinal column. The spine is made up of 33 vertebrae which form a column. The vertebrae are conventionally divided into three regions: the cervical (upper back and neck); thoracic (mid-back, contiguous with the rib cage); and, the lumbar (the lower back). Each region of the spine is responsible for implementing specific motions of the body. For instance, the cervical region provides a full range of rotation, whereas the thoracic region has limited rotation and lumbar region has restricted rotation. The entire spine can be flexed forward through "rocking", i.e., bending the entire spine, or "crunching" i.e., hingelike movement focused at the T10-L1 region of the spine.
Problems with the spine arise when regions of the spine are subjected to stresses or motions that are inconsistent with the function of that region. For instance, excessive rotation of the lumbar region vertebrae can cause damage to the intervertebral discs. Similarly, excessive lateral loading of .the cervical region can cause injury to discs. Improper movements can also overstress and fatigue related muscle groups.
When exercising the muscles of the abdomen and back, a primary source of concern is the safeguarding of the lumbar region of the spine. The lumbar spine movements are predicated predominately by the orientation of the facet joints. The facet joints on the lumbar vertebrae are flattened and essentially vertical "plates" on the sides of the vertebrae which interlock to restrict vertebral rotation. The primary movement in the lumbar spine is therefore flexion and extension with rotation limited when the facets are engaged. However, as the front flexes forward, the facets are disengaged in the mid-range of flexion thereby permitting slight vertebral rotation. As the trunk flexes past the mid-range of trunk flexion, the facet joints are once again engaged thereby restricting the extent of vertebral rotation. In addition, when the intervertebral joints are subjected to the stress of weight-bearing or of motion, small movements of the joints, known as "strain deflections" result.
As emphasized in H. F. Farfan, Mechanical Disorders of the Lower Back, Lea & Febizer (1973), it is "generally conceded that it is virtually impossible to have a pure movement in any of the three principal planes [i.e., bending, twisting, leaning]. The orientation of the facet surfaces generally does not coincide with the plane of the motion and therefore modifies the motion of the intervertebral joint. This is more certainly true of rotation than it is for flexion or extension. In an individual with symmetrical vertebrae, movements in the A-P plane may be free of either lateral bend or rotation. However, rotation is not possible without some degree of flexion and lateral bend." Thus, with reference to Farfan, it may be seen that the "crunch" motion, even in an individual with a symmetric spine, defines a complex curve or arc for a given joint as the spine is flexed through its entire range of motion. Consequently, as flexure occurs in the lower lumbar region, vertebral rotation and strain deflections occur which cause stress to lumbar spinal discs.
Therefore, when performing abdominal or back exercises it is desirable to minimize or eliminate flexure or extension in the lower lumbar region. This can be accomplished by restricting flexure of the spine to the T10-L1 region of the spine by performing a proper crunch motion and avoiding a rocking motion. Because the T10-L1 region is the "hinge" portion of the spine it is less likely to suffer rotation or strain deflections during flexure.
Performance of "crunches" or situps can have equally deleterious effects on the cervical region of the spine. Unless the head is supported during these exercises, the lateral stresses on the head and neck i.e., the hanging of the head will rapidly fatigue the muscles supporting the head. The result of the muscle fatigue is additional stress on the vertebrae and intervertebral discs.
In sum, as conventionally performed, i.e., free hand, abdominal and back exercises are not without hazard and inconvenience. Performing free hand sit-ups while keeping the legs straight risks injury and pain due to undue stress on the lower back regions. There is also danger of straining the hip flexor muscles and difficulty of controlling or adjusting muscular resistance. Performing free hand knee-ups also risks injury to the lower back and hips. Unless the knees are kept bent, the back is always curved and the abdominal muscles are tensed, thereby increasing the stress to the lower spine. Also, both free hand sit-ups and most exercise devices tend to create the undesirable rocking motion rather than the desirable hingelike or curling flexure of the back associated with a proper "crunch". The increased radius of flexure associated with rocking creates excessive movement in the lower lumbar region-of the spine allowing undesirable strain deflection and rotation. Furthermore, at the upper portion of the movement associated with a "crunch," the head tends to hang down, which can cause fatigue or discomfort in the neck.
There are few free hand exercises comparable to sit-ups or crunches which exercise the muscles in the back. Thus, individuals tend to over-exercise the abdominal muscles and under-exercise the back muscles, which can lead to discomfort and fatigue as a result of imbalanced musculature. As with situps and kneeups, the conventional reverse situps generate excessive flexure of the back creating a potential for injury. The free hand reverse sit-up is uncomfortable as it generally involves a support placed under the abdomen resulting in excessive pressure to the gut. Also, the inverted position of the body and head, can result in discomfort and dizziness. As in the free hand crunch or sit-up, the neck is without support, resulting in fatigue and discomfort in the neck as well as a potential for injury to the cervical discs.
Therefore, to minimize the risk of injury as well as achieve a greater level of comfort and control compared to that resulting from performing free hand abdominal and back exercises, there has been a need for a device and/or technique whereby a person can perform the crunch motion while performing repetitions of exercises equivalent to sit-ups, reverse sit-ups and/or knee-ups, but while remaining within safe limits of stress to the neck, back and abdominal muscles.
Various resistance-type exercise devices for exercising abdominal muscles are known. However, it has been found that when a person undertakes a program of conditioning the abdominal or back muscles by systematic use of such a device, that person often soon abandons the program because the resistance is so great as to allow performing only a few repetitions before fatigue sets in, or so small that the muscles are not adequately stressed regardless of how many repetitions are done. Even if the resistance is initially in an appropriate range for a user's muscular strength, he or she may find that as his or her muscles become stronger through exercise, that a conditioning plateau is reached where the set resistance is insufficient to provide further strengthening, thereby necessitating a need for a means to progressively increase or vary the resistance.
As is well-known, the preferred method for strengthening muscles is exercise using progressively increasing resistance because this places increasing demand on muscles and prevents them from accommodating to a specific force. Thus, to enable a resistance-type device to be used effectively by people having different strength, and to enable an individual who progresses through an exercise program to remain challenged as his or her strength increases, there is also a need for an abdominal and back exercise device which not only meets the above-stated criteria, but also one in which resistance can be conveniently increased or decreased.
Also, the general practice is to use a different device to exercise each targeted muscle group. This increases the complexity and cost of the exercise facility because of the multitude of different devices required to achieve a complete coverage of exercises. Thus, it is desirable to provide a single exercise device that can provide more than one exercise function, targeting more than one muscle group.
Devices for exercising the abdominal muscles are known. For example, U.S. Pat. No. 5,122,107 to Gardner describes a device which provides support to the head and neck of an individual performing sit-ups. U.S. Pat. Nos. 5,308,306 and 5,300,005 to Wang describe devices to provide assistance to an individual performing sit-ups. U.S. Pat. No. 5,256,126 to Grotstein describes a device to exercise muscles of the abdomen and back. U.S. Pat. No. 5,346,447 to Stearns describes devices for performing a multitude of exercises using the users weight for resistance.
Each of the above described devices address individual problems associated with performance of crunch motion exercises. As noted above, however, there are numerous problems which exist in conjunction. In order to provide effective and safe exercise these problems must be addressed in conjunction. Furthermore, the described devices generally involve large, complex and expensive machinery targeted at only one mode of exercise.